1. Field of the Invention
The present invention relates to a light emitting element having a layer including an organic compound between a pair of electrodes and a light emitting device using the light emitting element.
2. Description of the Related Art
In recent years, a light emitting device including an electroluminescence element as a self-light emitting element has been researched and developed. In particular, a light emitting device, which utilizes a so-called an organic electroluminescence element where a layer including an organic compound that emits light by applying an electric field, has features of a high response speed suitable for an moving image, low voltage driving, low power consumption driving, and the like. Therefore, the light emitting device utilizing an organic electroluminescence has been attracted as a display including a cell phone, a portable information terminal (PDA), and the like of the next generation.
The light emitting element described above is formed with a layer including a light emitting substance interposed between a pair of electrodes (an anode and a cathode). As emission mechanism thereof, when a voltage is applied between the both electrodes, holes injected from the anode and electrons injected from the cathode are recombined with each other in a luminescent center in a layer including a light emitting substance to form molecular exciton. Then, when the molecular exciton returns to a ground state, the molecular exciton releases energy to emit light. It is to be noted that singlet excitation and triplet excitation are known as an excitation state. It is considered that light emission can be performed through singlet excitation or triplet excitation.
Recently, a driving voltage has been remarkably improved. For example, a composite layer of a metal oxide such as vanadium pentoxide or dirhenium heptaoxide and an organic compound is to be a hole injecting layer; whereby an energy barrier when injecting holes from an anode to an organic compound layer can be reduced (see Patent Document 1: Japanese Patent Application Laid-Open No. 2005-123095).